How to save Child Of relative transform to absolute
In the list of keying sets you will find several "Visual" options, these options keyframe values of the visual location/rotation/scale, which is after constraints have been applied.



The only explanation for visual keying I can find is in the keyframing preferences, where you can make this the default behaviour.


  When an object is using constraints, the object property value does not actually change. Visual Keying will add keyframes to the object property, with a value based on the visual transformation from the constraint.